Restoration planning for urban salmonid habitat: Effects of stormwater runoff on water quality and benthic invertebrates

Restoration of salmonid habitat has been completed in many urban areas; however, the success of these projects may be limited without consideration of water quality. Urban watersheds are affected by stormwater runoff which transfers toxic substances such as heavy metals, hydrocarbons, and fine particles from impervious surfaces into streams. Previous research has documented impacts of stormwater causing premature death in spawning coho (Oncorhynchus kisutch), and related extent of impervious surfaces to impacts on benthic invertebrates. This research aims to expand our knowledge on the effects of stormwater runoff on water quality and benthic invertebrate communities, and make recommendations for restoration of Mosquito Creek, in North Vancouver, British Columbia. Stream water quality was monitored, site habitats were assessed, and impervious surfaces were mapped. Benthic invertebrate samples were collected and analyzed for abundance, diversity, and pollution tolerance, comparing upstream and downstream of a stormwater inflow and two sites on a reference stream. Average water quality measurements showed minor impacts related to elevated temperatures. However, benthic invertebrate metrics revealed chronic water quality issues, reflecting cumulative impacts. Pollution tolerance index and abundance were reduced at the downstream Mosquito Creek site suggesting impacts from the stormwater inflow, while the Ephemoptera, Plecoptera, Trichoptera (EPT) to total ratio and overall stream health (Streamkeepers Site Assessment Rating) were significantly lower at Mosquito Creek overall suggesting watershed impacts from impervious surfaces and point-source pollution events. Restoration recommendations including a rain garden are discussed to improve water quality for salmonids.